This invention relates to xerography, and more specifically to an improved photoreceptor device for use in a xerographic process. The improvement constituting the subject matter of this application is a means for obtaining an injecting contact at the interface of the photoconductor layer and the base of the photoreceptor, the photoconductor layer comprising minute photoconductor particles supported by and dispersed within an insulative resin matrix.
The present invention has particular application in connection with a photoreceptor device having a photoconductive phase such as is described in Jones U.S. Pat. No. 3,787,208, with or without a dielectric overcoating, depending upon the ultimate xerographic process in which the photoreceptor is to be applied. This type of photoconductive material will hereinafter be referred to as "controlled geometry" photoconductor material.
Controlled geometry photoconductor material is fully described in the above Jones patent, to which reference may be made for a complete understanding of a photoreceptor using this material and the various processes by which it may be obtained. For purposes of the present application, suffice it to say that the controlled geometry photoconductive material comprises a photoconductive insulating layer comprising an insulating organic resin matrix and a photoconductive material, with substantially all of the photoconductive material lying in a multiplicity of interlocking photoconductive continuous paths through the thickness of the layer. The photoconductive material constitutes from about 1 to 25% of the photoreceptor layer, and the interlocking path arrangement of the photoconductive material is achieved by controlling the bulk geometry of the layer. In brief, relatively larger resin particles are merged with significantly smaller photoconductive particles so that the latter occupy the interstitial space of the packed resin particles. This general relationship of the particles remains during and after the resin curing operation wherein a carrier liquid (not a solvent for either the resin or photoconductor particles) is removed from the assembly and the resin particles are bonded together at their areas of contact. The size of photoconductor particles in the controlled geometry system may vary, but as disclosed in the Jones patent, is preferably in the order of 5 times smaller than the resin particles, or smaller, usually in the range of 0.01 to 1 micron, preferably about 0.5 microns, depending on the desired order of resolution required and the ultimate xerographic process in which the photoreceptor layer is intended for use.
The present invention also has particular utility in an electrophotograhic imaging process using the controlled geometry photoconductor layer with a translucent or transparent dielectric overcoating wherein the dielectric layer is first surface charged to a high potential of opposite polarity to the photoconductor mobile charge carriers; the overcoated photoconductor is exposed to a light and dark image pattern while the surface of the dielectric layer is charged with a reverse polarity field or an AC field to produce at uniform surface potential a charge density pattern corresponding to the light and dark image pattern; and finally uniformly illuminating the overcoated photoreceptor to increase the charge potential in the dark areas of the image pattern and thereby improve the contrast ratio in the final developed image. The thus charged photoreceptor is capable of remaining charged with the image pattern when illuminated as well as in the dark and can be developed using any conventional xerographic process. This imaging process is more completely described in U.S. Pat. Nos. 3,794,539 and 3,775,104, for example, and does not constitute per se the subject matter of the present invention. In this process it is essential that the first charging create a potential only across the dielectric layer and not across the combination of dielectric layer and photoconductive layer. Therefore, since the charge carriers on the photoconductive layer must freely be energized from the backside of the photoconductor layer to enable the migration of charges from the base of the photoreceptor to the interface between photoconductive and dielectric layers, a charge injecting contact between the base and photoconductive material is absolutely essential to enable the initial charging of the dielectric layer to occur in cyclic fashion.
It has been learned, however, that in circumstances where an insulative matrix is used to carry the photoconductive material, and where the latter is provided as particles of extremely small size, the necessary injecting contact between the photoconductor material and base is prevented by a layer of resinous matrix between most, if not all, of the photoconductor particles and the conductive base. The exact mechanism by which the photoconductor particle to base contact is lost is not fully understood, but is believed to be caused by the inability of the small photoconductive particles to overcome the surface tension of the resinous material in which the small particles are carried. This has particularly been observed where the photoconductor layer is formed by a controlled geometry method.
The present applicant has discovered that an injecting contact between the photoconductor and the base layer can be provided to overcome the problem, while at the same time achieving a suitable bond between the two layers. In short, both a means for achieving this injecting contact and the method of its fabrication constitute the subject matter of this invention, in an environment such as has been set forth above.
The present invention therefore has as its primary objective the provision of an injecting contact between a photoconductor layer and conductive base layer in a unique manner that enables the contacts to be made while a controlled geometry photoconductor layer is being made.